- Not so good at brewing coffee
- Seriously, none for what you pay for

Got this one second-hand about a year ago, after it was apparently hand-picked out of a batch of (an arbitrary number between 4 and 8).
My lens of choice in almost all circumstances (except when I use my Canon 70-200 f4) on a 20D. I own the Canon 50mm f1.4 as well (upgraded from the 1.8), and I RARELY use it. The Sigma almost never leaves my camera!

Focusing is fast (Hunts far less than the canon 1.4 in low light), sharpness is very good at f1.4 and Skyrockets at smaller apertures. Fantastic for low light conditions and isolating subjects. 1.4 is tricky to focus at, but this is a limitation of the photographer, not the lens.

Slight softness around the edges at low aperatures, but I can live with that. Quality control might be an issue, so I suggest you buy this one in person and make sure you get a good copy (I tested a few and the focusing differs significantly)

I absolutely adore this lens, and I would suggest it to anybody who takes the time to ask...